Method and apparatus for producing sheet material



May 4, 1943. E. R. bERBY .ET AL METHOD AND APPARATUS FOR PRODUCING SHEETMATEB IAL Filed Feb. 16, 1959 izuen for."

Patented May 4, 1943 UNITED STATES PATENT OFFICE METHOD AND APPARATUSFOR PRODUCING SHEET MATERIAL Elmer R. Derby, Springfield, Mass andFrederic A. Parkhurst, Suflield, Conn., assignors to Monsanto ChemicalCompany, St. Louis, Mo., a corporation of Delaware Continuation ofapplication Serial No. 142,352, May 13, 1937. This application February16, 1939, Serial No. 256,696

1 10 Claims.

The present application is a continuation of our application forApparatus for producing sheet material, filed May 13, 1937, Serial No.142,352. The present invention relates to a method and apparatus forforming a continuous web, sheet or ribbon from plastic material, suchwebs being of question ar thermoplastic and our novel method differentthicknesses according to the use to accordance with the processdescribed in the application of Gustavus J. Esselen and Elmer R. Derbyfiled February 16, 1939, Serial No. 256,732.

It is desirable in the manufacture of these ma-' terials into sheets'forcertain purposes that the gauge be extremely uniform andin the case ofsandwich material for laminated glass, the variations in gauge must notexceed 0.001 inch in one inch of length or breadth. In the manufactureof plasticized cellulos nitrate sheet-stock to be used as sandwichmaterial for laminated glass it has been found practical to form acontinuous web by extruding the stock by means of a rotary die, forinstance, such as is shown in the patent to Parkhurst No. 1,881,917,dated October 11,-1932,

and in connection with the manufacture of plasticized cellulose acetatea straight slot die, such as is shown in the patent to Parkhurst No.

2,061,042, dated November 17, 1936, may be used. However, it has notbeen found practical to use the procedure described in these patents forthe manufacture of plasticized polyvinyl acetal resin, nor in themanufacture of thin transparent contlnuous web of any of thesematerials. The plasticized polyvinyl acetal resins are relatively soft,but are extremely tough and rubbery. They resist permanent deformationand tend to return to I their original form and shape for a long timeafter having been deformed. They are tacky-on the surface and adhere tometallic smfaces. These properties appear to have a definite efiect ongauge. None of the procedures mentioned have been found satisfactory inthe manufacture of thin transparent webs, sheets or ribbons having athickness of less than 0.005 of an inch.

However, we have discovered that it is possible to produce material of asatisfactory gauge from the substances mentioned and in gauges varyingfrom-below 0.005 of an inch to upwards of 0.050 of an inch and to do soat rates of from 10 to 60 linear feet per ,minute. All of the materialsin takes advantage of their thermoplastic properties. We have found thatif a suitable'mix is made, which in some cases is made with smallamounts of volatile solvent and is heated to'increase its plasticity,and this mix is then extruded into contact with a smooth travellingsurface such as a roller or polished endless belt of a temperatureenoughlower than that of the mix to set the portion of the mass as it contactswith the travelling surface, and that practically simul-- taneously themass, while still on the travelling surface, is passed under a heatedmember conveniently called a die blade the temperature of which is highenough to maintain or possibly increase the plasticity of the mix, asheet of extremely uniform gauge and, in the case of certain materials,having highly polished surfaces on both sides may be produced. We arenot en-v tirely certain as to the exact action of the heated die bladewhich forms the surface'opposite to that formed first by the travellingsurface, but it is possible that at the instant the sheet passes outfrom under the heated die blade, its surface is sufficiently fluid sothat the surface tension of the material has some effect in reducingin-- equalities and enhancing the-polish of the sur face. Our presentmethod is particularly eifective in producing sheets from completelycolloided materials. Since the particular features of the method offorming such high polished transparent sheets from completely colloidedmaterials of this kind are separate, inventions, no claims thereto areincluded herein.

One apparatus embodying our invention and preferably used for thepractice of our novel method is shown in the accompanying drawing:

Fig. 1 is a. front elevational view of an appa ratus embodying theinvention, partly' broken. away,

Fig. 2 is a sectional elevational view taken on the line 2-2 of Fig. 1;and

Fig. 3 shows diagrammatically means for supporting the die blade.

Before explaining in detail the present invention it is to be understoodthat the invention is not limited in its application to the details ofconstruction and arrangement of parts illus- The apparatus illustratedin the accompanying,

drawing comprises a hollow casing to having a cylindrical chamber H towhich plastic material is supplied through one end thereof. This casingis of novel construction and is the subject of a separate applicationfor Letters Patent. The

casing III also is provided with a passage l2 extending laterally fromthe passage I The walls of the passage l2 taper toward one another andterminate adjacent the surface of a roll 20. If desired, a bridge orscreen H may be interposed in the passage l2.

, At each of its ends the casing I is provided with a forwardlyextending projection IS in which are formed suitable bearings forrotatably sup-- porting the die roll 26 so that its periphery 2| closelyengages the surface of the casing on one side of the passage l2 andprevents any flow of is parallel to a tangent to the roll 20. This plate25 is secured upon the casing III by bolts 26 extending through slots 21in the plate 25 and engaging the casing Ill. The position of the late 25may be adjusted toward and from the roll 20 and toward and from the wall22 by screws 30 threaded in the casing l0 and engaging the top edge ofthe plate 25. The screws 30 may be locked in desired position by locknuts 3|. The space between the die blade 25 and the roll 20 forms theextrustion slot which is a primary factor in determining the thicknessof the web produced and the character of its surface.

.A take-off roll 36, the periphery of which is spaced from the peripheryof the roll 20 a distance corresponding to the thickness or gauge of thesheet or web being produced, is rotatably supported in bearings inbrackets 35 secured to extensions I5.

- The casing I0 is provided with heating means here shown as a waterjacket 50 embracing'the chamber The casing may also be provided withwater Jackets 5| extending above and below the passage l2. A waterjacket 62 is provided in the plate 25 near the roll 20. The main roll 20as well as the take-off roll 36 are hollow and may be supplied withwater for controlling their temperature through axial passages 60 and 6|respectively. Preferably, the rolls 20 and 36 are posi- P tively rotatedand for this purpose may be connected through gears 63 and 64 suppliedwith power from any, suitable source. In order to assist the removal ofthe web W of sheet material from the main roll 20, a compressed airnozzle 66 is provided adapted to force air under pressure between theweb W and the periphery 2| of the roll.

Assuming that the plate 25 has been adjust ed to the desired positionwith respect to the roll 20, plastic material is supplied under pressureto the chamber through one end thereof and thence is forced through thepassage I2 and is extruded through the orifice l3 directly upon theperiphery of the roll 26 in the form of a thin web W. The web W is movedaway from the orifice by the rotationof the roll20 and later is removedfrom the roll 20 by the take-off roll 36 and is led to .an-'

other point for further treatment or storage.

Roller 48, having axle 62, is rotatably supported by frame 4|, which,with strengthening crosspiece 42, is rotatable about the axis of mainroll 26 to adjustable positions about the exterior thereof, asillustrated in full lines and dotted lines in Fig; 2. Roller 46 isrotated by gear wheel 65 in contact with gear wheel 63 of main roll 20.

For purposes of illustration the following examples of mixes of basematerials, together with the temperatures to be employed at the severalpoints of the machine are given as follows:

Example 1.A polyvinyl acetal resin is made by combining a partiallyhydrolyzed polyvinyl acetate with butyraldehyde under such conditions asto give a product containing approximately 18- 20% uncombined polyvinylalcohol, 1-2% poly-' vinyl acetate and the balance substantially acetal.This is mixed with 43 parts of triethylene glycol dihexoate to eachparts of the vinyl acetal resin. No volatile solvent is used.

The resin and plasticizer are mixed together in any convenient type ofmixer as, for example, a jacketed kneading machine and the mass isagitated until it takes on a sponge-like consistency. If this mixingoperation is carried on at a temperature of approximately F. theoperation takes about one hour fora batch of 200 to 300 lbs. of resin.The resin is put in the machine first and the plasticizer is then pouredin, being distributed as well as possible. Where two or moreplasticizers are used they are mixed in the required proportions beforebeing added to the resin.

After the mixture has assumed the uniform sponge-like consistency it istransferred to a Banbury mixer which is at a temperature of approxi--mately 180 F. Within two or three minutes the batch begins to decreasein volume, loses its spongy quality and begins to weld into a tough,translucent mass. Cold water is then circulated through the jacket ofthe Banbury mixer and mixing is continued for from twelve to fifteenminutes longer after which the entire mass will have become tough andrubbery. Even though cold water has been circulated through the jacketof the mixer theintemal heat raises the temperature of the mix toapproximately 280 F. at this point. The material is now ready to befiltered or strained.

The tough, rubbery mixture, prepared as described above, is fed inchunks of about 15 lbs. each into the cylinder of a hydraulic strainer.With each addition the mass is packedv tightly by a packing ram. Themass as it comes from the mixer is usually opaque due to the presence ofair bubbles but during the packing of the straining cylinder the greaterpart of the entrapped air is forced out and the opacity decreases.

The mix is forced through a fine chrome steel screen backed by a Monelmetal screen. Particles of dirt and foreign matter are removed by thesefilter media. The strainer plate which supports the filter media isheated to between 240 to 310 F., the lower temperature range beingpreferred.

The cylinders of the hydraulic strainers are heated to between 160 and220 F., about 180 F. being preferred.

From the outlet of the hydraulic strainer the filtered stock heated asdescribed is fed under pressure to the chamber ll of the machine shownin the drawing. In this machine the temperature of the body of themachine, housed by easing I0 is maintained between 280 and 320 F.,preferably about 300 F., and the die blade 25 is maintained between 230F. and 280 F., about 240 F. being preferred; the die roll 20 ismaintained at about 120 to F., about 130 F. being preferred, thetake-off 36 is maintained between and 200 F., about 180 being preferred.Since the temperature of the die roll 20 is lower than that of the dieblade 25 and the casing III, the stock when it first contacts with thesurface of the die roll as it emerges from the orifice [3 in the casingis chilled and begins to harden while the portion of the stock which isin contact with the die blade 25 is maintained in a relatively hot and,therefore, more plastic condition. The temperature of the stock at themoment of sheet formation, 1. e. when it passes under the die blade, isdifllcult to ascertain because as stated, it is not uniform throughoutthe thickness of the sheet. Before contacting with the die roll 20, thetemperature of the stock is between 160 and 220 F., preferably about 200F. For some formulations where the quantity of plastici'zer is increasedand the plastic is consequently more heat sensitive, a downward revisionof 10 to 20 F. in temperature is allowed. Although the die roll 20 ismaintained at a temperature above that of the atmosphere, it has, asalready pointed out, the

Parts Cellulose acetate (37.5 to 38.5 per cent acetyl) 100 D1 (methoxyethyl) phthalate 15 Diethyl phthalate 15 Acetone 15 Denatured alcoholcontaining 5 to 6% of water by volume 24 Ethyl acetat 24 In preparingthis mix the cellulose acetate is charged into a jacketed kneadingmachine heated to 118 F. The solvents and plasticizers are weighed andmixed and added to the cellulose acetate-in the mixer while stirring.After about 40 minutes, the direction of rtoation of the mixing paddlesis reversed for about five minutes to insure that no pockets ofincompletely mixed materials have been found, after which the mixingpaddles are again reversed to normal mixing di- F rection and mixingcontinued for another 20 minutes. F. after about 40 minutes mixing andis kept at this point throughout the remainder of the mixing cycle bysupplying hot or cold water to the mixer jacket as required. 1 Thevmixture thus prepared is completely colloided and is formed into asheet by the machine shown in the drawing. In this case the temperatureof the casing 10 is, maintained between 150 F. and 200 F., preferablyabout 175 F., the die blade 25 is maintained between 120 F. and 180 F.,about 135 F. being preferred; the die roll 20 is maintained at 80 F. to140 F., about 120 F. being preferred, and the take-off roll ismaintained between 40 F. and 120 F., about 65 F. being preferred. Thetemperature of the stock before contacting with the die roll 20 is at atemperature between 120 F. and 200 F. preferably about 160 F. Thepressure in the casing behind the die orifice I3 is maintained between350 and 600 pounds per square inch. These operating conditions apply toa particular extrusion unit operating on the mix described and producinga transparent ribbon at a ribbon The temperature of the batch reaches160 plastic.

speed of from 10 to 60 feet per minute, the. stock being .005 inch inthickness.

It should be recognized that there is an interdependence betweentemperatures, pressures and speeds and that they are a function of thesize of the unit as well as the properties of the While it has beenimpossible to ascertain exactly what takes place at the time of sheetformation, it seems probable that the chilling effect of the die roll 20tends to stiffemor set one face.

of the web as it is being formed, while the other face is stillmaintainedin a soft plastic condition and is being formed by the dieblade 25 and that as. the softer surface emerges from under the diebladeit tends to flatten out and to assume a highly polished surface. Atany rate,

with completely colloided stock,'such as is described in Example 2, itis possible to produce webs or ribbons both surfaces of which have ahigh gloss orv polish.

What is claimed is: a I

1. The method of making continuoussheets of thermoplastic material whichcomprises heating the thermoplastic material sufflciently to increaseits plasticity and thereby render it more readily formable, forcing thematerial continuously through an orifice formed between a continuouslymoving continuous surface and a fixed member extending in contact withsaid material only slightly beyond the point of initial contact of thematerial with the moving surface, said moving surface extending beyondsaid fixed member and being sufllciently cooler than the material toharden the surface of the material as it contacts therewith, and saidfixed member being maintained at a temperature higher than that at whichthe material solidifies too much 7 to be formed, so that the fixedmember gives form to the softened face of the web being formed thecooled moving surface so that one surface of the web being formed ischilled and supported by said moving surface as the web passes saidheated member which gives form to the other,

surface of the web, and continuing contact of the formed web with saidmoving surface after said web has moved beyond said heated member. .1 3.The method of making a continuous web of thermoplastic material whichcomprises heating the thermoplastic material sufiiciently to in-.

surface, said moving surface extending beyond said stationary blade,maintaining said moving surface at a temperature less than that of saidmaterial so as to chill and set one face of the web, and maintainingsaid stationary blade at a temperature above that at which said materialsolidifies too much to be formed, and continuing contact of the formedweb with said moving surface after said web has moved beyond saidstationary blade.

4. The method of making a continuous web of. thermoplastic materialwhich comprises heating the material sufficiently to increase itsplasticity and thereby render it more readily formable, forming the webby forcing the softened material between two members, one of which iscontinuous and continuously moving and which forms an orifice with theother member, the other member extending in contact with said materialonly slightly beyond the point of initial contact of the softenedmaterial with the moving member, said moving member extending beyond theother member, cooling the moving member, and maintaining the othermember at a temperature higher than that at which the materialsolidifies too much to be formed, and continuing contact of the formedweb with said moving member after said web has moved beyond the othermember.

5. The method of making a continuous web of thermoplastic material whichcomprises heating the material sufiiciently to increase its plasticityand thereby render it more readily formable, forming the web by forcingthe softened material between two members, one of which is continuousand continuously moving and wziichforms an crifice with the othermember, the other member extending in contact with said material onlyslightly beyond the point of initial contact of the softenedmaterialwith the moving member, said moving member extending beyond the othermember, cooling the moving member to harden one said feed means, astationary member located adjacent said pressure feed means and saidcontinuous moving surface and forming in combination an extrusionapparatus having an orifice extending only slightly beyond the initialpoint of contact with said moving surface of the thermothermoplasticmaterial which comprises in combination pressure feed means providedwith heating means, a continuous moving surface adjacent said feed meansand a stationary blade located adjacent said feed means and saidcontinuous moving surface and forming in combination an extrusionapparatus having an orifice extending only slightly beyond the point ofinitial contact of the thermoplastic material with said moving surface,said moving surface extending beyond said stationary blade, means forcooling the moving surface adjacent said blade sufficiently to hardenthe thermoplastic material as it contacts with the surface thereof,means for heating the stationary blade, and means spaced apart from saidblade for maintaining the formed web in int'imate contact with saidcontinuous moving sursurface of the web while the other surface incontact with said other member is maintained softened and engaging theother member, heating said other member while it is giving form to theweb, and continuing contact of the formed web with said moving memberafter said web, has

moved beyond said other member.

6. The method of making a continuous web 0 thermoplastic material whichcomprises heating the thermoplastic material sufilciently to increaseits plasticity and thereby render it more readily formable, forming theweb by forcing the plastic material between two members, one of which iscontinuous and continuously moving and whichforms an orifice with theother member, said other member extending in contact with the web onlyslightly beyond the point of initial contact of the plastic materialwith said moving member,

said moving member extending beyond said other the formed web with saidmoving member after said web has moved beyond said other member.

7. An apparatus for making continuous webs of thermoplastic materialwhich comprises in combination pressure feed means provided with heatingmeans,-a continuous moving surface adjacent face after extrusion throughsaid orifice.

9. An apparatus for making continuous webs of tion an extrusionapparatus having an orifice extending only slightly beyond the point ofinitial contact of the thermoplastic material with said rotatingsurface, said rotating surface extending beyond said fixed member, meansfor cooling the continuous rotating surface adjacent said fixed membersufliciently to harden the thermoplastic material as it contacts withthe surface thereof,

means for heating the fixed member, and means spaced apart from saidfixed member for.maintaining the formed web in intimate contact withsaid continuous rotating surface after extrusion through said orifice.

10. An apparatus for making continuous webs of thermoplastic materialwhich comprises in combination pressure feed means havin a heattheformed web in contact with said movable surface after extrusion throughsaid'orifice.

ELMER R. -DERBY. FREDERIC A. PARKHURST.

